We Might Finally Know the Cause of a 500-Year-Old Epidemic

When Spanish conquistadors arrived in the Americas, they brought many things that changed the lives of the people that lived there: guns, Christianity, colonialism. But perhaps the thing that had the biggest impact was brought completely by accident: disease. Soon after the Europeans arrived, disease outbreaks killed millions of people across both continents.

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One of those outbreaks occurred in Mexico soon after the arrival of Hernán Cortés and his soldiers. In 1545 and again in 1756 a plague swept through Mexico, killing millions of people. Unfortunately, there’s little evidence of what that plague actually was. Theories range from smallpox to measles to some unknown virus that we’ve never seen before.

But thanks to some archaeological investigating, we might finally have some idea of what caused it. A team of researchers found DNA from a bacteria, Salmonella enterica, in a grave of some of the victims from the outbreak, meaning there’s a good chance that this bacteria is what caused it.

Most people in the developed world are probably familiar with salmonella as a food-borne pathogen, but it’s also the cause of a deadly disease called paratyphoid fever. Paratyphoid exhibits many of the same symptoms as regular typhoid fever, and it can lead to the same kind of disease outbreaks as the more well-known version.

Of course, just because salmonella was found in the bodies of the victims doesn’t mean that the bacteria was responsible for the outbreak. In particular, the sheer number of people that died makes it a little hard to believe that a common bacteria like salmonella was involved. But there really isn’t any better hypothesis with as much supporting evidence, so right now this is the best thing we’ve got. Unless scientists find any more evidence in the future, it’s likely that this case is pretty much settled.

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